Organic Light Emitting Diode (OLED) is one of the focuses in the field of flat panel display research. Compared with the liquid crystal display, OLED has the advantages of low power consumption, low production cost, self-light emission, wide viewing angle and fast response. At present, in mobile phones, PDAs, digital cameras and other display fields, OLED has begun to replace the traditional LCD display. Among them, the pixel circuit design is the core technology of OLED display, and has important research significance.
Unlike LCDs that use a stable voltage to control illuminance, OLEDs are current driven and require a constant current to control light emission. Due to manufacturing process and device aging and other reasons, the threshold voltage Vth of the drive transistor of the pixel circuit has unevenness, which causes the current flowing through the OLED in each pixel point to change thereby resulting in uneven display illuminance and thus affecting the display effect of the entire image.
FIG. 1 is a schematic circuit diagram of a pixel circuit in the prior art. As shown in FIG. 1, taking an existing pixel circuit with two transistors and one capacitor (2M1C) as an example, the circuit comprises one drive transistor M2, one switch transistor M1, and one storage capacitor Cs. When a pixel circuit of a certain row is scanned, a low level signal is inputted to the scan line Scan of the pixel circuit of this row, the P-type switch transistor M1 is turned on and the voltage of the data line Data is written into the storage capacitor Cs. When the scanning of this row is completed, the signal inputted into the scan line Scan becomes high level, the P-type switch transistor M1 is turned off, and the gate electrode voltage stored by the storage capacitor Cs causes the drive transistor M2 to generate current to drive the OLED and ensure that the OLED continuously emits light within one frame. The saturation current formula for the drive transistor M2 is IOLED=K(VSG−Vth)2. As described above, due to manufacturing process, device aging and other reasons, the threshold voltage Vth of the drive transistor M2 will drift, and furthermore, due to IR Drop, the source voltage VS of the drive transistor M2 may also vary. This causes the current flowing through each OLED to vary as the threshold voltage Vth of the drive transistor and the voltage VDD applied at the source of the drive transistor vary, resulting in unevenness in illuminance of image.